1. Field of the Invention
This invention relates to the field of medical devices. More particularly, this invention relates to an indwelling catheter assembly for use in hemodialysis.
2. Background Art
Hemodialysis catheters are used to remove waste products such as potassium and urea from the blood, such as in the case of a patient with renal failure. A first catheter conducts blood away from the patient through dialysis extension tubing to a dialysis machine where the blood crosses a semipermeable dialysis membrane to a balanced salt solution, which purifies the blood. A second catheter conducts the purified blood back from the dialysis machine to the circulation of the patient. Thus, while undergoing dialysis, a patient's blood circulates not only through his/her own body, but also through the dialysis machine circuit comprising the first and second catheters, dialysis extension tubing and the machine itself. In hemodialysis, both the arterial and venous access catheters are threaded into the same high flow, high pressure access site, albeit at somewhat spaced apart locations therein. A hemodialysis site may be either an AV fistula or a graft. An AV fistula is a surgically created area, usually on a patient's forearm, where blood flows just beneath the surface of the skin at high pressure and speed. An AV fistula is created by joining an artery directly to a vein, thereby artificially bypassing the normal (low pressure) capillary blood system. This causes high pressure arterial blood to pour into a normally low pressure vein, which causes the vein to distend and grow much larger. During hemodialysis, both the arterial access catheter and the venous access catheter are inserted into the patient's AV fistula, but the arterial access catheter is placed four to five centimeters upstream from the latter. That arrangement prevents mixing of cleansed blood with uncleansed blood at the AV fistula because the cleansed blood that is returned from the dialysis machine back to the patient is thereby carried away from the uncleansed blood that is being drawn up into the dialysis machine. If a patient's veins are in poor condition, a graft may be used as a hemodialysis site instead. A graft comprises an artificially-created loop of a synthetic material, such as Gortex (registered mark), that joins an artery directly to a vein. As in the case of an AV fistula, a graft will also present high pressure, high flow blood at the patient's hemodialysis access site, and placement of the arterial access and venous access catheters is performed similarly to that for an AV fistula. The hemodialysis catheter assembly of the present invention is intended for use with patients who have an AV fistula access site as well as those who have a graft hemodialysis access site.
Prior to my invention, access to a patient for hemodialysis has been gained by use of a dialysis catheter of simple design, consisting of nothing more than a sharpened, hollow, stainless steel needle and its attached extension tubing. Kidney dialysis patients typically require three dialysis sessions each week, and each dialysis session usually lasts three to four hours. As a result, repeated access must be gained to the patient's blood circulation over periods of time extending sometimes for years, and there is necessarily a continuing concern to avoid damaging the patient's hemodialysis access sites with the conventional sharpened, hollow, stainless steel needles at those sites. This is all in contrast to an intravenous (IV) catheter, which consists of a sharpened, hollow, stainless steel needle inserted within the lumen of a flexible, Teflon® sleeve or cannula for attachment to low pressure venous blood flow. The hollow, sharpened, steel needle of an intravenous catheter is carefully advanced into a patient's vein. Then the hollow, steel needle portion of the IV catheter is withdrawn, and the remaining Teflon® cannula is connected to a set of external, intravenous tubing for its use as an IV access site. This leaves the flexible Teflon® cannula of the intravenous catheter in the place of a sharpened steel needle, thereby reducing damage to the walls of veins for patients receiving IV therapy. The normal procedure for placing an intravenous catheter is to withdraw the sharpened, hollow, steel needle from the lumen of its flexible Teflon® sleeve after the successful engagement (cannulation) of a vein. During the time that the needle has been withdrawn and before the catheter has been connected to intravenous tubing, the open end of the catheter is exposed to room air at normal atmospheric pressure. The greater pressure within the venous circulatory system causes blood to slowly trickle out from the open end of the catheter. Because pressures within the venous circulatory system are relatively low, not much blood is lost this way. It is a common practice to exert a bit of pressure from a gloved finger placed just above the site where the blood flows through the lumen of the intravenous catheter. This point of resistance stops the trickle of blood from leaving the open end of the catheter until a set of IV tubing can be connected to it.
It would be highly advantageous, therefore, when performing hemodialysis on a patient, to substitute the flexible, Teflon® cannula/sharpened, hollow needle combination that is used in IV therapy for the dialysis catheter that has heretofore been used to gain access to a patient's hemodialysis site. A hemodialysis catheter having a flexible Teflon® tip would cause less trauma to the walls of blood vessels for patients receiving multiple sessions of hemodialysis. Reducing damage to these access sites would help extend the sites' functional life spans, and would significantly reduce the frequency of access-related complications arising out of hemodialysis therapy. But, as a practical matter, such a substitution cannot be done because of the difference in the pressure of the blood at an intravenous access site compared to the pressure of the blood at a hemodialysis access site that connects to the arterial side of the patient's blood circulatory system, because the arterial side has relatively high blood pressure—i.e., five to six times higher than an intravenous access site. If one attempts to use an intravenous catheter as a hemodialysis catheter, the higher pressure encountered on the arterial side of a patient's blood circulatory system will cause blood to rush out from the open end of the catheter at high speed. This would obviously create a hazard for the healthcare workers, exposing them unnecessarily to the patient's blood and to possible contamination by blood-borne pathogens. Furthermore, patients who receive dialysis therapy are predisposed to a condition that limits their ability to produce red blood cells. This condition is related to the pathology of kidney failure, so that nearly all hemodialysis patients who require regular dialysis therapy must also carefully manage their red blood cell count. Excessive blood loss is of particular concern for patients on hemodialysis and must always be avoided. Accordingly, the practice of holding a gloved finger and applying pressure just above the site where blood flows through the lumen of a hemodialysis catheter on the arterial side of a patient's blood circulatory system, in an attempt to control bleeding through the catheter, would not arrest the flow of blood from the open end of such a catheter. The pressures within the lumen of the catheter would be too great to be overcome by such a simple mechanical procedure. Unlike an intravenous catheter connected to a low pressure, venous access site, the catheter connected to the arterial side of a hemodialysis patient would continue to bleed profusely until one managed somehow to connect it to hemodialysis tubing, and so to secure a closed circuit. In addition, physicians are averse to having any sort of pressure or occlusion placed over these specially created hemodialysis access sites. They are artificially made avenues of high pressure blood flow created surgically just beneath the surface of the skin, and as such they are far more prone to clotting, and therefore to ruin, than′ any naturally formed blood vessel. Consequently, the practice of maintaining pressure over a hemodialysis access site in an attempt to control the loss of blood is to be avoided.
U.S. Pat. No. 7,252,652 B2 issued to Moorehead et al. disclosed a pressure-activated, two-way slit valve assembly for use in combination with a high flow rate, hemodialysis catheter. The valve assembly could be attached to a catheter having a single lumen or alternatively multiple lumens, and included a flexible, normally closed, thin disk disposed normal to the direction of blood flow through the assembly. The disk was sized to enable the slit to deform in response to a predetermined blood pressure differential across the slit to allow blood to pass through the slit, which flow could be either away from the patient toward a dialysis machine or toward the patient from a dialysis machine, depending upon the direction of the pressure differential.
Patent Application Publication US2009/0281525 A1 of Harding et al. disclosed a device with integrated flow control capabilities for controlling fluid flow through an indwelling catheter assembly, intended for use in artificial dialysis, among other applications. A catheter adapter body having a hollow, interior space or lumen was coupled to an end of a catheter. A flexible, normally-closed septum disposed within the interior space of the catheter body could be opened to permit flow through the catheter body by depressing an exterior, flow control button disposed within a window opening of the catheter body adjacent to the septum. In one embodiment, the septum comprised a normally-closed slit that could be opened to permit flow whenever the septum was inwardly deformed by depressing the button. Alternatively, insertion of a probe, such as a hollow needle, into the interior space of the catheter body and through the slit would also open the slit and permit flow through the catheter adapter body. In an alternative embodiment, the septum was impermeable and had no slit; instead, the septum was positioned within the lumen of the catheter adapter body so as to form a fluidtight interface between the septum and the inner surface of the catheter adapter body. Depressing a flow control button comprising a contact surface coupled to a shaft caused the shaft to displace the septum and disrupt the interface between the septum and the inner surface of the adapter body, thereby permitting fluid flow through the gap between the outer surface of the septum and the inner surface of the adapter body.
The above-referenced devices of Moorehead and of Harding et al. are not really suitable for use in hemodialysis because they fail to adequately address the problem of turbulence in blood flowing at high speed and under high pressure through the relatively small internal channel (lumen) within a dialysis catheter. Excessive turbulence can cause red blood cells to break open, rendering them useless to the patient and possibly contributing to electrolyte imbalances within the blood stream. To avoid turbulence, the internal surfaces of a hemodialysis catheter must be smooth, gradually tapered and seamlessly connected with one another.
Three of the four versions of the device disclosed by Harding et al. include ribbing on the surface of a septum actuator, which ribbing will create excessive turbulence within the body of their catheter. In an alternate version disclosed by Harding et al., the ribbing is absent, but the inner walls of the catheter gradually taper just past the point where a flexible septum crosses the lumen of the catheter and is joined together with the internal walls of the catheter body. This tapering would cause any probe capable of fitting within the catheter body and which is used to bias the septum to stop short of joining flush with the window that connects the septum chamber to the rest of the catheter body and its extension lead. The failure of such a probe to join flush with this window will cause the inserted end of the probe to be exposed as an open step or open shelf within the lumen of the dialysis catheter. Blood rushing past this exposed shelf at high speed will be subjected to excessive turbulence.
Similarly, all five versions of the device disclosed by Moorehead fail to adequately address the problem of excessive turbulence. All five versions include multiple flow channels within a single lumen of a hemodialysis catheter. These include dumbbell-shaped, H-shaped, and saw tooth split channels. Such systems of narrow channels create excessively turbulent flow of blood through the lumen of a catheter under the high pressure, high speed flow conditions encountered at a hemodialysis access site. Furthermore, such systems of channels create high back pressure that slows the progress of filtration and circulation in a dialysis machine circuit.
Harding's device includes a push button disposed over the top of the hemodialysis catheter body, which must be pressed down in order to permit blood to flow through the catheter. Hard pressure applied to the button causes hard pressure to be applied over the surface of the hemodialysis access site. That is an unacceptable practice, as it is well known that such hard pressure can lead to complications with the access site itself.
The thin, dual membrane septum assembly disclosed by Harding et al., which is intended to permit blood flow in one direction only, is likely to weaken with use and begin to deform to permit blood flow in an opposite direction through the septum assembly. The result could be escape of blood through the open lumen of Harding's dialysis catheter just as easily as blood could enter into it.
My hemodialysis catheter assembly, however, avoids these problems. It is capable of reliably arresting blood flow even under high pressure, high speed blood flow conditions and without creating excessive flow turbulence. It does not create back pressure within the dialysis machine circuit, and it does not create any unnecessary pressure or occlusion across the surface of a hemodialysis access site.